There is a long felt need for an efficient chemical or polymeric compound that can impart both oil/grease- and water-sizing properties to paper. Many grades of paper require both oil/grease resistance and water resistance. Commercially available chemicals that are said to provide both oil/grease- and water-sizing properties are not in fact efficient water-sizing agents. A separate water-sizing agent must be added along with the oil-sizing agent when high levels of both oil/grease and water resistance is desired. Oil/grease- and water sizing agents often have a negative impact on each other's performance, so when both oil/grease- and water sizing properties are desired, higher levels of each are required relative to when only one of the properties is needed.
A general discussion of oil and water sizing of materials appears in the article, Waterproofing and Water/Oil Repellency,” Kirk-Othmer Encyclopedia of Chemical Technology, John Wiley & Sons, New York, 1984, Volume 24, page 442. In particular, there is a discussion of the use of contact angle measurements for judging the degree of wetting or repellency for a liquid on a plane-solid surface. On pages 448 and 458 there is discussion of uses of fluorocarbon chemicals to improve repellency.
Materials containing perfluorocarbon segments have long been utilized to impart oil and grease repellant properties to a wide variety of substrates, including cellulosic materials such as textiles and paper (e.g. Sizing with fluorochemicals, R. D. Howells, 1997 Sizing Short Course, Nashville, Tenn., April 14-16, TAPPI Press, Atlanta). Perfluoroalkyl-substituted chemicals possess extremely low free surface energies, making them particularly effective at repelling low surface energy materials such as oil and grease, thus preventing staining of the substrate surface or spreading of the oil or grease over the substrate surface. For these materials to function effectively and without detriment to the paper and textile manufacturing process, they must generate minimum foam, not deposit on the manufacturing equipment, and be effectively retained and evenly distributed on the substrate. For practical commercial applications they must also form stable dispersions. Some examples of end-use applications include pet-food bags and boxes, fast food packaging, pizza boxes, candy wrappers, carbonless paper, packaging for fatty foods in general, molded board for paper plates, etc., carpet, upholstery and other textiles applications and leather goods.
Commercial papermaking conditions require that any chemical additive, such as a sizing agent, must be either readily water dispersible in its neat form, or easily convertible into a water dispersible emulsion or stable aqueous dispersion. There are two physical forms of sizing agents in aqueous delivery systems: dissolved or dispersed ionic salts and dispersions or emulsions of particulates or oils. Sizing agents in particulate form must be low melting solids, very small size particles (submicron), or liquids so the material will spread throughout the paper when heated in the dryer section of a paper machine.
When the sizing agent is added to the pulp slurry (internal addition) it must adhere to the pulp or it will not be retained in the paper. This may be accomplished by means of opposite charge attractions between the pulp and the size and by physical trapping of particles of size during web formation.
Although there are compounds described that claim to provide oil/grease- and water sizing most are less effective against hot oil and ineffective when exposed to hot water. The performance of existing technologies is limited by the temperature of the oil/grease that the paper comes into contact with. The repellency of the paper falls off considerably as the oil/grease temperature increases which limits the applications that substrates treated with oil/grease-sizing agents can be utilized economically.
In order to thoroughly evaluate oil/grease- and water-sizing agents, extensive testing procedures must be utilized. The most prevalent screening test is the TAPPI T559 pm-96 or the so-called Kit Test. An extended range Kit Test was used to develop/understand this invention. Even though the test only measures the nonpolar component of surface energy it can be useful as a quick test to monitor treatment levels after the selection of type of fluorochemical sizing agent and method of application has been determined.
Correlation to real end-use performance is required. In general, it is important to match the test liquid to the nature of the fluid that must be controlled to prevent staining. In addition to the fluid, for a good test of a sizing agent the temperature and other environmental conditions also need to simulate the end use of the paper. Thus, many tests were used to evaluate and develop a full understanding of the compounds and polymers described by this invention.
While commercial products and products described in literature, especially the patent literature, often provide oil sizing, none of these compounds/polymers have the combination of both efficient oil/grease- and efficient water size over ranges of temperature required for a breadth of commercial applications. None meet the performance criteria achieved by this invention.
Polymers of perfluoro-allyloxy and perfluoroalkyl-iodo propyloxy substituted polyamino acids or poly-RF-fluoroallyl substituted polyamino acids are described in U.S. Pat. No. 6,156,222. While this reference teaches the use of these compounds in grease-proofing paper, none of these compounds have the epihalohydrin or epiorganosulfonate reaction fragment functionality, and thus the resultant cross-linking and cellulose reactive capability.
In International Publication No. WO 90/02110, Szonyi describes a perfluoroalkylated amino compound, which has been adducted with epichlorohydrin. There are only two nitrogens in these perfuoroalklyated diamino compounds. In all examples and revisions to the claims in the application file Szonyi describes the nitrogen at which the epi reacts as tertiary, which would not allow the formation of the 3-hydroxyazetidinium group. Szonyi's publication does not describe the secondary nitrogen atom required for the invention described herein for formation of the 3-hydroxyazetidinium group.
In International Publication No. WO 00/43438 perfluoro alkyl-substituted polyamino acid consisting of oligomers/copolymers of aliphatic diamino carboxylic acid—having 3 to 10 carbon atoms and containing at least two perfluoroalkyl groups attached to nitrogen atoms through a linking group are described. Essential features are the limitation of two amino group per monomer unit and that there be a pendant carboxylic acid group, that is in the amino acid chemical structure.
An epoxidized amide-amine fluoro compound is taught in Great Britain Patent #1,214,528. A key feature of this compound is that in the backbone there is an amide linkage and there is no hydrophillic group that should stabilize an aqueous dispersion.
Thus, in spite of efforts to produce a material that provides both efficient oil/grease sizing and efficient water sizing to cellulosic products, these efforts have only partially given the combination of sizing needed. The invention described herein is especially useful when the treated paper must withstand hot oil/grease- and/or hot water environments.